Radiobroadcast distributing system



Aug. 14, 1928.

2 Sheets-Sheet F'ILTEB Moor/Mme lwuomtw Filed Nov. 25, 1925 I Q '9 o F/LTEE z E E CLEMENT RADIOBROADCAST DISTRIBUTING SYSTEM .1 Monaura Aug. 14,1928. v 1,681,100

S i E. E. CLEMENT RADIOBRO ADCAST DISTRIBUTING SYSTEM Filed Nov. 25;1925 2 Sheets-Sheet 2 CZ a FILTER MODl/LA T012 Patented Aug. 14, 1928.

entree stares EDWARD E. GLEMENT or WASHINGTON,

area-tee PATENT-r@rrrcag DISTRICT or coLnMBI nssrelvoa 'ro En H WARD F.COLLADAY, F wasmnerom mstrnlor oncoLUMBIa.

nanronnoancnsr DISTRIBUTING SYSTEM,

pr I i v i nppl ication filed November um My invention relates to radiobroadcast distribution,. and its objects are secrecy,-

flexibility and certainty. [It achieves'transmission by What I havecalleda silent wave, because there would be no intelligiblemanifestation in any ordinary receiving instrument of the modulations,being transmitted by this system. It supplies the final link in thechain of operations of the system dis- 0 closed in my prior copending'application, Serial No. 746,357, filed October28, 19245,

patented July 5, 1927, as No. 1,635,153, in

which it was stated thatthe use of double modulation would enablesecrecy to be at-. tained, and in which the selection of programs withthe fixed or flat tuned instrument was attained by tuning the secondarycircuit so as to take off and select one of several intermediatefrequency carrier waves, all modulated on a carrienwave or waves of thesame standard high frequency, to which the receivers are tuned, and eachbearing a different audio frequency modulation of its own. 3 I

Y I attain my objects 'by'first producing by modulation at audiofrequencies in the presence of an intermediate. superaudio frequencysource, a band of frequencies representing the. said superaudiofrequency plus or minus the" constantly changing modulating audiofrequencies, thereby in effect producing frequencyfmodulation. I thenmodulate these waves at frequencies which are constantly changing 'astheir audio frequency component changesupon a wave of constant highfrequency,'. which thereupon becomes alsovariable in its frequencycharacteristic in'proportion to the strength of the carrier with respectto the strength of the variable frequency modulating band. I thenradiate. this doubly modulated carrier. At the receivingfstation ,I

first detect and demodulate the high freT- Jib original audiomodulations. r

As a modified method of practicing 'the inventionfI may follow theforegoing, but without having "a separate source to supply theintermediate frequency atthe receiving mediate frequency carrier. to nobtain the 25, 1925; Serial No! 71,456..'

station. Instead thereof, I may separately modulate the originalintermediate. frequency carrier wave on a suitable highfrequencycarrierwave, radiate thesame, re,- ceiveit at the receiving station,demodulate, and, apply the resultant intermediate frequency current tothe composition circuit to combine with. the variable frequency Wave;

band as before. I y

My inventionis illustratedin the accompanying drawings, in Which T ition equipped with a balanced primary modulator circuit, a bandfilter'and we ondary modulatorcircuit of the Colpitts- Heising type bywhich. a doubly modulated short wave carrier is radiated to thereceiving'station, having the characteristics of a Fig. 1 is a diagramof a transmitting Sta-f variable frequency modulation instead of i theusual variableamplitude modulation.

Fig. 2 is a diagram of a receiving station adapted to cooperatewith thesending station of Fig. 1, and provided with a source of'altcrnatingcurrent capableof giving the same, frequency as that originally suppliedin the primary modulating circuit of l.- Fig. 3 is a diagram ofamodifiedarrangement, using the simple Heising method for double modulation,withan interposed filter.

- Fig. 4 is a schematic' diagram showing the same system as'in Figsland2, but with it separate radio transmission of the original low frequencycarrier wave, for supply to the demodulator atthe receiving station,

Fig. .5 is a schematic diagram illustrating a "modification of thevariablefrequency band modulation, using balanced modulatg ing-circuitswith band filters for both modue.

lators. v 1

Referring toFigs; 1'. and 2, represents a transmitting station and Yrepresent-a receiving station. In Fig.- 1, mis ,a balanced alternating'superaudio frequency being 0011-.

modulator circuit in, which there is nor-. mally no currentfflow, thesource S of ion nected by 'couplerfi to theneutral member 7 of thebalancing circuits 2-3, through which the sameipotential is maintainedonthe grids of both vacuum tubes V and V.". When variable currents arecaused to flow int-he audio ;.frequency circuit '1', as hy microphoneT,--the balance is"disturbe'd, and I plate circuits t- 57" carry bandsof'waves ofthe frequency'of S plus and minus the varying audiomodulation frequencies, but

' without any 'unmodulated current of frequency S above. '10 is a filterbywhich one band maybe suppressed, and'one bandeni-y passed to thesecondary modulator wt. Gou 1 plings 8 and 11 are of any desired :and:suit-p able type. The modulator circuit 12 and tube V and theoscillator :circuit \13 tube S are of a usual type, adapted to imposethe Wave band passed through cou pling 11, on the oscillatory carrierwave produced by S andto' radiate the latter from antenna circuit 14." I

"The sources may generate current of a I frequency from 25 to 100kilocycles per sec- 0nd, "w hich I have designated herein as superaudioY frequencies or IF i e. intermediate frequencies, lying betweenaudioand "radio frequency limiter,

The source. S generates oscillating current at radio frequency, forexample, at a frequency between '500 and 3,000 kilocyclesper second. it

It is to be understood that these figures areIgiVen for purposes ofdefinition of the invention, and not'for limitation, as they may 'bevaried without departure therefrom if the principle of bandnmodulationorra radio carrier not the same as the original carrier is" maintained.As a matter of fac t,; the "oscillator S and its immedlate circuit m y*be' replaced by a harmonic generator,

'or' harmonic producer" such as 'adistortion tube, takingits-initialenergiza'tionfrom the low frequency generator S. This would repledjamplifier and power circuits. v

- 'In Fig. '2, 7 is the first demodulator and duce the modulatorpractically to, couz/ "theseco'nd demodulator; "Si is a source.

of super-audio "frequency current "equivalent to that supplied'bygenerator S. It is shown ascoupl'edgtoth'e second detector "circuitbyaficoil in inductive relation to the (30118 of the 'coup'ler '28, butmay be-connected instead through aseparate composition an 7cuit"25,'f(see Fig. 4), interposed between thefelementsof coupling 28 inFig. 2. The

antenna circuit 15 is tuned,"-'asqis the input circuit .17, to receivethe band'modulated carrier radiated from 14 in; Fig. l. The firstdetector Y :demodul'a-tesrthis rad-io carrim, and passes the modulatedyariablefrequency band'through' coupler 281:0 the input- 21 of thesecond-detector "V curren'tfromthe-source S being also supplied throughsaid circuit to the gridv circuit20. This 1F or superadio frequencycurrent acts upon the incoming modulated wave band :to tran late itgfroma band of-variable frequencies 2 to a variable amplitude"modlilation onthe IF carrier current, -whic1h is rectified by the second detector Vand the signal modula the known Heisi-ng type," with can Arnold filter1O interposed between them to-sup- 1, however, is thepreferredarrangement.

press the unmodulated carrier currentsu'pplied-.i-by oscillator 1S, :andamplifiers} for the -.-ba=nd-;passed to the modulator tube V f Inimyapplication filed concurrently here- I with, SerialNo. 71,457, filedNovember 25,

mitting and receiving station's similar to that shown"here1n but w thawire c rcu t 'conducting cui'rent from the source (Fig.- v 1), to the"coinposition"circuitor coil 28or 25*(Fig's11 21and4) so thatthe'generator S is unnecessary, and the frequencies-S ends in circuits 7and2l are identical, In the present case I do 'not 'show any wirecircuit,

but in order to ensure the 'syn'chronism and modul'aterw,fas[b S, and tothe circuit 21 or 2 5 asby S", may modulate a second radioffrequencycarrier wave withmthe IF or =1ntermed1ate frequency {from generator Sand radiate "the same to stations Y where it 'is'demodulate'cland the IFwave amplified and supplied to composition circuit 2501' 21,

1 instead of current separately generated at S, {Such an arrangement isschematically illustrated in Fig. 4, infwhich, as before, X

is atransmitting station'an'd Y is a receiving stationi At station X therectangle a; represents the balanced modulatorthe same as mediatefrequency or superaudio potential by generator S. i The'microphone'setsup audio frequency alternations in the circuits pliase identity of thewaves supplie'dto'the i that shown in Fig, 1, supplied with inter-f 2and"3 "whi'ch ffunction in the presence of said superaudio potential toproduce a'wave band of frequencies varying-inaccordance with "the; audioorother'rnodulation imposed on *circuit 1'; (This band passes throughcoupler8 to'the band filter and amplifier 10,

thence through coupler 11' t0 the modulator and' amplifier a whereby itisjinodulated as ibefore on a radio carrier wave 'and finally radiatedfrom the circuit 14.

' addition "to its connection through coupler f6 to "themodulator w, thegenerator Shas 'aiseries couplerj'connection 11 with a modulator and"radiator' m supplied with high Q or radio frequency carrier current "bygenerator-SSW. iT-his1unitaz actsto impose the nnmodulatedjconstant"frequency wavedue to"S on"t he'radio carrier wave; due to 5 'andthen toradiate this carrier'inodulated with'a'carri-er;

- at stationY the operationof the first m1 second demodulations g a'n'd'y/"is'the sameas before described, but instead of a separate f carrierwave-generator for the composition circuit 25, I provide the'sepa'ratedemo'dmlater and amplifier unit 1 3 "which receives same, andafter-z amplification :to the extent desired, :supplies th-e frequencywave the wave 'ra'diate d by wfl demodulates' the,

lac

thus derived from S, through circuit 26 and where it acts upon the waveand passed by coupling 20, to translate the same from a band of variablefrequencies to amplitude modulations on the IF carrier, which beingpassed through coupling 20 to the second detector circuit 3 isdemodulated and the signal modulations communicated with or withoutamplification, to the responsive device 23. Thus, the wave band carryingthe signal is radiated on one carrier, andthe IF wave on which the waveband wasmodulated, is itself radiated on another carrier, both arereceived and separately detected and then combined.

In Fig. 5 I have shown schematically a modified arrangement oftransmitting and receiving apparatus in which balanced modulatorcircuits similar to that marked at in Fig. 1 are used for bothw and so,with wave filters and amplifiers 10 and 1 OOfor their respectiveoutputs. The parts are marked with the same numerals and letters. as before. Modulations or signals as by T, are propagated in the circuits 23and func tioning in presence of superaudio or IF alternating potentialsfrom generator S produce variable frequency bands at 8 which a singleside band is passed by 10, amplified if desired, and through coupler 11communicated to circuits 200 and 300, second modulator m which areidentical with circuits 1 and 2 of w. This wave band modulation,functioning in the presence of radio frequency alternating potentialfrom generator S produces at 11 two side bands, from which one is againfiltered out and amplified at 100 and radiated from the circuit 14. Thereceiver Y has an antenna circuit 15 tuned to receive the compound bandof variable frequency, and an amplifier and composition circuit 25,supplied by generator S with current of frequency the same as S Theeffect ofthis composition is to pass through coupler 2O a carrier offrequency S carrying amplitude oscillations representing the modulatedband due to m. The first detector 3 detects off this IF wave band,

which varies in frequency in accordance with the variatlons 1n thesignal frequency imposed by T or other signal transmission.

This band is then passed through coupler 20 to amplifier and compositioncircuit 250 (similar to 25) supplied by generator S with intermediatefrequency current of the same frequency as S, and the resultantmodulated currentis passed through coupler 20 to the final detector anddemodulator y which delivers the signal modulations to the responsivedevice 23.

' In this circuit of Fig. 5, it is necessary to tively. This makes itvery desirable to use a means of supplying the same current or potentialfrom generator S to both in and 1,! (through 250) and from generator Sto both :0 and y (through 25). Such a means is the wire circuit ornetwork described in my application Serial No. 71,457, filed November25, 1925, a'bove referred to;'or the method of radiating theintermediate frequency carrier shown in Fig. 4 herein. The use 0 suchmeans I consider novel and original with myself and to be claimedaccordingly.

It will be understood that all proper expedients and agencies known inthe art are contemplated and to be applied to these circuits inpractice, such as suitable filters, amplifiers, current control devices,etc., none of which I have shown in detail, for of simplicity.

What I claim is:

1. A radio broadcasting system comprising a primary or audio frequencymodulator adapted to function in the presence of an alternatingsuperaudio frequency carrier po- 'tential, to produce a band ofsuperaudio frelated waves upon a radio frequency carrier wave, and aradiator for radiating the same, means to impose an unmodulated waveequivalent to the original superaudio carrier, as a modulation on aradio frequency carrier wave and to radiate the same, with a receivingstation equipped with a first and a second demodulating circuit, andmeans to demodulate the last named carrier and to supply theintermediate frequency or superaudio component thereof to the saidsecond demodulating circuit together with the audio modulated wave bandfrom the first demodulating circuit.

2. The method of radio transmission of signals which consists in doublymodulating a carrier wave by first modulating signals on a relativelylow frequency carrier and suppressing the unmodulated carrier'so' as toleave only a side band, and then modulating this side band upon a highfrequency high frequency carrier and radiating the I same.

In testimony whereof I hereunto afiix my signature.

EDWARD E. CLEMENT.

the sake I es

